Disk roll and base material for disk roll

ABSTRACT

The present invention provides a base material for disk rolls which is a platy molded article for obtaining ring-shaped disks for use in a disk roll comprising a rotating shaft and ring-shaped disks fitted thereon by insertion, whereby the peripheral surface of the disks serves as a conveying surface, the base material comprising inorganic fibers having a crystallization temperature of 800-900° C., a filler, and a clay. Also disclosed is a disk roll which comprises disks cut out of the base material.

This application is a divisional of application Ser. No. 12/801,166filed May 26, 2010, now allowed, which in turn is a continuationapplication based on application Ser. No. 11/727,447 filed Mar. 27,2007, now U.S. Pat. No. 7,781,043, which in turn is based on and claimspriority to JP 2006-100490 filed 31 Mar. 2006, the entire contents ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a disk roll which comprises a rotatingshaft and ring-shaped disks fitted thereon by insertion, whereby theperipheral surface of the disks serves as a conveying surface. Moreparticularly, the invention relates to a disk roll suitable for use inproducing a high-quality glass plate. The invention further relates to abase material for disk rolls which is for use in producing therefromdisks for the disk roll.

BACKGROUND OF THE INVENTION

In the production of a glass plate, a conveying mechanism is necessaryfor glass plate formation from a molten-state glass or for annealing theglass plate formed. This conveying mechanism generally comprisesconveying rolls, and disk rolls are being used as one species of suchconveying rolls.

FIG. 1 is a diagrammatic view illustrating a disk roll 10 as an example.This disk roll 10 is produced in the following manner. An aqueous slurrycontaining inorganic fibers, a filler, a clay as a binder, and otheringredients is formed into a sheet by a papermaking method and dried toform a platy material having a thickness of about several millimeters.Ring-shaped disks are punched out of the resultant dried base materialfor disk rolls, and these disks 12 are fitted by insertion onto ametallic shaft 11 serving as a rotating shaft. Thus, a roll-form stackis obtained. The whole stack is compressed through flanges 13 disposedrespectively on both ends, and these disks 12 in this slightlycompressed state are fastened with nuts 15 or the like. In the disk roll10 thus obtained, the peripheral surface of the disks 12 functions as aconveying surface.

Such disk rolls 10 are mounted in a glass plate production apparatus 100as shown in FIG. 2, and used for glass plate formation and conveyance.This glass plate production apparatus 100 is an apparatus in which amolten glass 110 is continuously discharged from a melting furnace 101through a linear slit 102 of the furnace, and this strip-form moltenglass 110 discharged is caused to descend and is cooled and hardenedduring the descent to thereby produce a glass plate. The disk rolls 10function as a pair of drawing rolls, which hold the strip-form moltenglass 110 therebetween and forcedly send it downward. The disk rolls 10just after the production thereof are constituted of disks 12 obtainedby merely shaping the aqueous slurry. When the disk rolls 10 in thisstate are used for conveyance, the clay is sintered by the heattransferred upon contact with the molten glass 110. The disks 12 thusharden, and strength and wearing resistance are imparted thereto. Thehardening proceeds with repetitions of contact with the molten glass110.

Alumina fibers and aluminosilicate fibers are extensively used as theinorganic fibers from the standpoint of heat resistance. Alumina fibersand aluminosilicate fibers crystallize upon heating or thecrystallization thereof proceeds with heating, whereby these fibrousmaterials increase in hardness. Although alumina fibers andaluminosilicate fibers can contribute to an improvement in wearingresistance through the hardening thereof, neither the alumina fibers northe aluminosilicate fibers crystallize at the surface temperature of themolten glass 110 (about 800° C.).

A disk roll containing mica particles which are incorporated in order toimpart heat resistance and wearing resistance has been proposed (see,for example, patent document 1). However, with the formulations usingalumina fibers or aluminosilicate fibers, the contribution of thesefibers to wearing resistance is not great as stated above.

-   Patent Document 1: JP-B-59-28771

SUMMARY OF THE INVENTION

An object of the invention, which has been achieved under thosecircumstances, is to provide a disk roll which has a well balancedcombination of heat resistance, wearing resistance and flexibility, andwhich is satisfactory in these properties.

Other objects and effects of the invention will become apparent from thefollowing description.

In order to accomplish the object, the invention provides the basematerial for disk rolls and the disk roll shown below.

(1) A base material for disk rolls which is a platy molded article forobtaining ring-shaped disks for use in a disk roll comprising a rotatingshaft and ring-shaped disks fitted thereon by insertion, whereby theperipheral surface of the disks serves as a conveying surface,

the base material comprising inorganic fibers having a crystallizationtemperature of 800-900° C., a filler, and a clay.

(2) The base material for disk rolls according to (1) above, wherein theinorganic fibers are biosoluble fibers.

(3) The base material for disk rolls according to (2) above, wherein thebiosoluble fibers are coated with a phosphoric acid salt, a molybdenumcompound, a zinc compound, a polyamidine compound, or an ethyleneiminecompound.

(4) The base material for disk rolls according to any one of (1) to (3)above wherein the content of the inorganic fibers is 5-40% by mass basedon the whole amount of the base material.

(5) A disk roll which comprises a rotating shaft and, fitted thereon byinsertion, ring-shaped disks cut out of the base material for disk rollsaccording to any one of (1) to (4) above, whereby the peripheral surfaceof the disks serves as a conveying surface.

(6) The disk roll according to (5) above which has a compressiondeformation of 0.05-0.3 mm when a load of 10 kgf/cm is imposed on theroll surface at 800° C.

In the disk roll of the invention, the inorganic fibers contained in thedisks crystallize at the surface temperature of a molten glass.Consequently, upon contact with a molten glass, the inorganic fiberscrystallize simultaneously with sintering of the clay to form a surfacelayer having higher hardness and thereby impart excellent heatresistance and wearing resistance. In addition, due to theheat-insulating properties inherently possessed by the disks, heattransfer to inner parts of the disks during repetitions of contact witha molten glass is inhibited and, hence, the inner parts do not hardenexcessively and can retain moderate flexibility. Because of this, thedisk roll of the invention has a well balanced combination of heatresistance, wearing resistance and flexibility, and has a long life andhigh performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view illustrating one embodiment of the diskroll of the invention.

FIG. 2 is a diagrammatic view illustrating one example of applications(glass plate production apparatus) in which the disk rolls shown in FIG.1 are used.

FIG. 3 is a diagrammatic view illustrating the constitution of theapparatus used in the Examples for measuring compression deformation.

The reference numerals used in the drawings denote the followings,respectively.

-   -   10: Disk roll    -   11: Metallic shaft    -   12: Disk    -   13: Flange    -   15: Nut    -   100: Glass plate production apparatus    -   101: Melting furnace    -   102: Slit    -   110: Strip-form molten glass

DETAILED DESCRIPTION OF THE INVENTION

The invention will be explained below in detail.

The base material for disk rolls of the invention is a platy moldedarticle of a mixture of a clay, a filler, and inorganic fibers having acrystallization temperature of 800-900° C. (hereinafter also referred tosimply as “inorganic fibers”).

As the clay, use can be made of one which, when mixed with water, showsviscosity and plasticity and which has the property of sintering uponheating. With respect to the kind thereof, examples include Kibushiclay, Gairome clay, and fire clay. Of these, Kibushi clay is preferredbecause it has a high binding effect in sintering and has a low impuritycontent. Two or more clays can be used in combination according to need.

The clay may be one which has been regulated, throughseparation/purification, so that the content of components having aparticle diameter of 5 μm or larger therein is 30% by mass or lower,preferably 15% by mass or lower, more preferably 10% by mass or lower.With respect to the lower limit thereof, a clay containing entirely nocomponent having a particle diameter of 5 μm or larger is optimal. Suchclay particles which are fine and uniform in particle diameter exhibithigher binding ability and tenaciously bind other disk-constitutingmaterials.

Through the separation/purification, impurities also are simultaneouslyremoved. In general, the particle diameters of a clay, which is anatural mineral, can be regulated in some degree bypulverization/classification. However, clay products contain a largeamount of impurities and the impurities, in many cases, include oneswhich do not have susceptibility to sintering, such as, e.g., silica. Indisk rolls, sintering and resultant hardening proceed during use as aresult of contact with the material being conveyed, such as a moltenglass. However, the impurities not having susceptibility to sinteringcan be a factor which inhibits the hardening function. In addition, theimpurities include many hard substances and there is a possibility thatthe hard substances might mar the material being transferred, inparticular, a glass plate. The content of impurities is preferably asclose to zero as possible. However, in view of the actual circumstancesincluding labor and cost, the content of impurities is preferably 10% bymass or lower, especially 5% by mass or lower, more preferably 1% bymass or lower, based on the whole clay.

In regulating the particle diameters so as to be small and within thegiven range as described above and in removing impurities, it iseffective to employ wet-process classification as a method ofseparation/purification. By conducting wet-process classification, notonly impurities differing in specific gravity or size can be removed,but also a raw-material clay having smaller particle diameters and anarrower particle size distribution than in dry classification cangenerally be obtained while utilizing the phenomenon in whichsedimentation velocities vary with the particle diameter.

As the filler, use can be made of one which has heat resistance, doesnot show unnecessary reactivity with other compounding materials, anddoes not contain hard large particles. Examples thereof include talc,alumina powder, silica powder, highly purified wollastonite, andnon-plastic kaolinite. However, particles of a mica or vermiculite aresuitable. Micas are known to have high elasticity and be excellent inslip properties, wearing resistance, heat resistance, etc., and arematerials which have been industrially utilized from long ago in variousfields. In the invention, a mica may be added for the purpose ofenabling the disks to conform to the thermal expansion of the shaft. Ina disk roll, since the shaft 11 onto which the disks 12 are fitted asshown in FIG. 1 is made of a metal, this shaft 11 thermally expands uponexposure to high temperatures and extends in the axial direction. Inthis case, since the disks 12 have a lower coefficient of thermalexpansion than the metal, the disks 12 cannot conform to the elongationof the shaft 11 and are separated from one another. On the other hand,the mica, which has a layered structure made up of exceedingly thinlayers, releases crystal water upon heating to undergo crystalmodification. With this crystal modification, the mica tends to expandin the thickness direction for the layers. This expansion in the layerthickness direction enhances the conformability of the disks 12 to thethermal expansion of the shaft 11.

As the mica, use can be made of muscovite (K₂Al₄(Si₃Al)₂O₂₀(OH)₄),biotite, phlogopite (K₂Mg₆(SiAl)₂O₂₀(OH)₄) paragonite, lepidolite, or asynthetic fluoromica. However, muscovite, which releases crystal waterat about 600° C., i.e., a temperature lower than the surface temperatureof a molten glass, is preferred from the standpoint of the function ofenhancing conformability.

The average particle diameter of the mica may be 5-500 μm, and ispreferably 100-300 μm, more preferably 200-300 μm. When the mica has anaverage particle diameter within that range, it is highly elastic andhence effectively functions as plate springs to store the stressgenerated by compression with other compounding materials, inparticular, the inorganic fibers. Thus, conformability to the thermalexpansion of the shaft can be further enhanced.

Vermiculite generally contains crystal water and dehydrates uponexposure to high temperatures. Namely, it functions like a blowingagent. It is therefore preferred to use vermiculite which has beenburned beforehand at, e.g., 600-900° C. The average particle diameter ofthe vermiculite is preferably 5-500 μm as in the mica.

The mica and vermiculite may be used alone or in combination.

The inorganic fibers are not limited as long as they have acrystallization temperature of 800-900° C. Examples thereof include theinorganic fibers described in JP-A-2000-220037, JP-A-2002-68777,JP-A-2003-73926, and JP-A-2003-212596. Specific examples thereofinclude: inorganic fibers in which the total content of SiO₂ and CaO is85% by mass or higher and which contain 0.5-3.0% by mass MgO and2.0-8.0% by mass P₂O₅ and have a carcinogenicity index (KI value) asdetermined in accordance with German Hazardous Substances Regulations of40 or higher; inorganic fibers comprising SiO₂, MgO, and TiO₂ asessential components; inorganic fibers comprising SiO₂, MgO, andmanganese oxide as essential components; inorganic fibers comprising52-72% by mass SiO₂, less than 3% by mass Al₂O₃, 0-7% by mass MgO,7.5-9.5% by mass CaO, 0-12% by mass B₂O₃, 0-4% by mass BaO, 0-3.5% bymass SrO, 10-20.5% by mass Na₂O, 0.5-4.0% by mass K₂O, and 0-5% by massP₂O₅; and inorganic fibers comprising 75-80% by mass SiO₂, 19-25% bymass CaO+MgO, and 1-3% by mass Al₂O₃. Such inorganic fibrous materialsmay be used alone or as a mixture of two or more thereof. Thecrystallization temperature of inorganic fibers can be ascertained byexamining the fibers with a differential thermal analyzer (DTG-50,manufactured by Shimadzu Corp.) for exothermic peak attributable tocrystallization.

Of those inorganic fibrous materials, ones which have a solubility inphysiological saline, as determined by the method shown below, of 1% orhigher are called “biosoluble fibers” and are especially preferred inthe invention.

A method of determining the solubility of inorganic fibers inphysiological saline is explained. First, 1 g of a sample prepared bypulverizing the inorganic fibers to a 200-mesh powder and 150 mL ofphysiological saline are introduced into an Erlenmeyer flask (300 mL).This flask is placed in a 40° C. incubator. Subsequently, the Erlenmeyerflask is continuously shaken horizontally at a rotation speed of 120 rpmfor 50 hours. After the shaking, the mixture is filtered, and theresultant filtrate is analyzed by ICP emission spectroscopy to determinethe concentrations of silicon, magnesium, calcium, and aluminum elements(mg/L) contained therein. The solubility in physiological saline C (%)is calculated from the concentrations of the elements and from thecontents of the elements in the inorganic fibers before the dissolution(% by mass), using the following equation (1). With respect to theelement concentrations obtained by the ICP emission spectroscopy, theconcentration of silicon element is expressed as a1 (mg/L),concentration of magnesium element as a2 (mg/L), concentration ofcalcium element as a3 (mg/L), and concentration of aluminum element asa4 (mg/L). With respect to the element contents in the inorganic fibersbefore dissolution, the content of silicon element is expressed as b1 (%by mass), content of magnesium element as b2 (% by mass), content ofcalcium element as b3 (% by mass), and content of aluminum element as b4(% by mass).C(%)={(filtrate amount (L))×(a1+a2+a3+a4)×100}/{(amount of inorganicfibers before dissolution (mg))×(b1+b2+b3+b4)/100}  (1)

The size of the inorganic fibers is not particularly limited. However,from the standpoint of the strength of the disk roll to be produced, theinorganic fibers preferably are ones having an average fiber diameter of1-5 μm, preferably 3-5 μm, and a fiber length of 0.5-200 mm, preferably1-20 mm.

The clay, filler, and inorganic fibers may be mixed in the followingproportions. The proportion of the clay is 5-55% by mass, preferably20-40% by mass, based on the total amount of the base material. Theproportion of the filler is 5-60% by mass, preferably 20-55% by mass,based on the total amount of the base material. The proportion of theinorganic fibers is 5-40% by mass, preferably 20-30% by mass, based onthe total amount of the base material. When the ingredients are mixed insuch proportions, a disk roll retaining a well balanced combination ofheat resistance, wearing resistance, and flexibility is obtained.

For producing the base material for disk rolls, use can be made of amethod in which an aqueous slurry containing the clay, filler, andinorganic fibers is formed into a plate shape by a papermaking methodand this plate is dried. This method is preferred because it isefficient. In this operation, ingredients such as a coagulant aid,organic fibers, and organic binder may be incorporated into the aqueousslurry in a given amount. The coagulant aid, organic fibers, and organicbinder each may be known one.

In the case where biosoluble fibers are used as the inorganic fibers, itis preferred that a substance which forms a coating layer, such as,e.g., a phosphoric acid salt, a molybdenum compound, a zinc compound, apolyamidine compound, or an ethyleneimine compound, be incorporated intothe aqueous slurry in order to inhibit the fibers from dissolving in thewater. The amount of the coating-forming substance to be incorporated ispreferably 0.1-10% by mass, more preferably 0.3-6% by mass, based on thesum of the clay, filler, and biosoluble fibers from the standpoint ofsatisfactorily coating the whole biosoluble fibers.

Examples of the substance for forming a coating layer include inorganiccompounds such as phosphoric acid salts, molybdenum compounds, and zinccompounds and organic compounds such as polyamidine compounds andethyleneimine compounds. Examples of the phosphoric acid salts includealuminum tripolyphosphate, aluminum dihydrogen tripolyphosphate,aluminum metaphosphate, zinc phosphate, and calcium phosphate. Examplesof the molybdenum compounds include zinc molybdate, aluminum molybdate,calcium molybdate, calcium phosphomolybdate, and aluminumphosphomolybdate. Examples of the zinc compounds include zinc oxide.Examples of the polyamidine compounds include acrylamide, acrylonitrile,N-vinylacrylamidine hydrochloride, N-vinylacrylamide, vinylaminehydrochloride, and N-vinylformamide copolymers. Examples of theethyleneimine compounds include aminoethylene and dimethyleneimine.

The thickness of the base material for disk rolls can be suitablyregulated, and may be the same as those heretofore in use. In general,the thickness thereof is 2-10 mm.

The invention further provides a disk roll employing disks cut out ofthe base material for disk rolls described above. The disk roll may havethe constitution shown in FIG. 1, which can be obtained in the followingmanner. Ring-shaped disks 12 are punched out of the base material fordisk rolls described above. These disks 12 are fitted onto a shaft 11made of a metal (e.g., iron) by insertion to obtain a roll-form stack.The whole stack is compressed through flanges 13 respectively on bothends, and these disks 12 in this slightly compressed state are fastenedwith nuts 15 or the like. Thereafter, the periphery of the disks 12 isground so as to result in a given roll diameter to thereby obtain a diskroll 10.

In the disk roll 10 of the invention, the inorganic fibers in a surfacelayer part crystallize simultaneously with the sintering of the clayupon contact with a molten glass. As a result, the surface layer partcomes to have a higher hardness and better wearing resistance than thosein which clay sintering only has occurred. In addition, the surfacelayer comes to have enhanced heat-insulating properties and, hence, theheat of the molten glass is less apt to be transferred to inner parts,whereby moderate flexibility is retained. Specifically, the disk rollhas a compression deformation of 0.05-0.3 mm when a load of 10 kgf/cm isimposed on the roll surface at 800° C.

EXAMPLES

The invention will be explained below in greater detail with referenceto Examples and Comparative Examples, but the invention should not beconstrued as being limited to the Examples.

Examples 1 to 6 and Comparative Examples 1 to 4

Aqueous slurries containing the raw materials shown in Table 1 wereprepared. Each slurry was formed into sheets by an ordinary papermakingmethod to produce a disk-roll base material in sheets which haddimensions of 100 mm×100 mm×6 mm on a dry basis. The inorganic fibers Aare aluminosilicate fibers (SiO₂:Al₂O₃=(54-55% by weight):(45-55% byweight)), while the inorganic fibers B are biosoluble fibers comprising75-80% by mass SiO₂, 19-25% by mass CaO+MgO, and 1-3% by mass Al₂O₃ andhaving a crystallization temperature of 860° C. and a solubility inphysiological saline at 40° C. of 5.9%.

Disks having an outer diameter of 80 mm and an inner diameter of 30 mmwere punched out of each of the base materials for disk rolls, andfitted onto an iron shaft having a diameter of 30 mm and a length of 100mm by insertion. Both ends of each disk stack were fixed with nuts toproduce a cylindrical disk roll which had the constitution shown in FIG.1 and in which the disks had a compressed density of 1.2 g/cm³. Thisdisk roll was held in an 800° C. heating oven for 180 minutes, taken outof the heating furnace, and then placed on trestles 50 so that both endsof the shaft 11 were supported on the trestles 50 as shown in FIG. 3. Aload of 10 kgf/cm was imposed on the conveying surface, which wasconstituted of the disks 12, with an indentator 60 at a rate of 1 mm/minto measure the resultant compression deformation. The results obtainedare also shown in Table 1.

Disk rolls produced in the same manner were evaluated for wearingresistance in the following manner. Each disk roll was held in an 800°C. heating furnace for 180 minutes. Thereafter, the roll was rotated at10 rpm and rubbed against a friction material made of SUS. The amount bywhich the radius of the roll had decreased due to the rubbing wasmeasured as an index to wearing resistance.

Furthermore, disk rolls produced in the same manner were mounted in aglass plate production apparatus having the constitution shown in FIG.2. This apparatus was used to actually produce a glass plate. Thesurfaces of the glass plate obtained were visually examined for mars.

The results of those examinations are also shown in Table 1.

TABLE 1 Comp. Comp. Comp. Comp. Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Example 7 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Kibushi clay 20 2020 20 30 50 20 20 30 50 30 Inorganic fibers A 20 20 10 30 Inorganicfibers B 40 40 30 20 20 10 36.5 Aluminum tripolyphosphate 3.5 Mica 25 3545 35 25 25 45 35 25 25 Vermiculite 25 Organic fibers 10 10 10 10 10 1010 10 10 10 10 Organic binder 5 5 5 5 5 5 5 5 5 5 5 Compressed density1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 (g/cm³) Compressiondeformation 0.22 0.24 0.18 0.10 0.12 0.07 0.20 0.10 0.16 0.05 0.20 (mm)Number of mars in glass 2 0 0 0 0 2 0 4 4 10 2 surfaces (per m²) Wearingresistance (mm) 2.0 2.5 3.0 3.5 3.5 4.0 2.0 8.0 9.5 12.0 8.0Comprehensive evaluation excellent excellent excellent excellentexcellent good excellent poor poor poor poor Note) Each ingredientamount is in % by mass.

Table 1 shows the following. By incorporating the inorganic fibershaving a crystallization temperature of 800-900° C., disk rolls can beobtained which have practically satisfactory heat resistance and wearingresistance and have moderate flexibility which prevents the disk rollsfrom marring the glass surfaces.

While the present invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

This application is based on Japanese Patent Application No. 2006-100490filed Mar. 31, 2006, and the contents thereof are herein incorporated byreference.

What is claimed is:
 1. A base material for disk rolls, comprising 5-40%by mass based on a total amount of the base material of biosolubleinorganic fibers having crystallization temperature of 800-900° C. and asolubility in physiological saline of at least 1%, a filler, and asinterable clay in an amount of 5 to 55% by mass, wherein the inorganicfiber contains 75 to 80% by mass of SiO₂, 19 to 25% by mass of CaO+MgOand 1 to 3% by mass of Al₂O₃, and when a disk roll is formed from thebase material, the disk roll has a compression deformation of 0.05-0.3mm when a load of 10 kgf/cm is imposed on a disk roll surface at 800° C.2. The base material according to claim 1, wherein the sinterable claybinder has particles having a diameter of 5 μm or larger.
 3. The basematerial according to claim 1, wherein a coating-forming substance isapplied to the inorganic fibers in the base material in an amount of 0.1to 10% by mass based on a sum of the clay, filler, and inorganic fibers.4. The base material according to claim 1, wherein the filler iscontained in an amount of 5 to 60% by mass based on the whole (total)amount of the base material.
 5. The base material according to claim 1,wherein the inorganic fiber contains SiO₂, CaO, MgO and Al₂O₃.
 6. Amethod of producing a base material for disk rolls, the methodcomprising preparing an aqueous slurry comprising 5-40% by mass based ona total amount of the base material of biosoluble inorganic fibershaving a crystallization temperature of 800-900° C. and a solubility inphysiological salien of at least 1%, a filler, and a sinterable clay inan amount of 5 to 55% by mass, wherein the inorganic fiber contains 75to 80% by mass of SiO₂, 19 to 25% by mass of CaO+MgO and 1 to 3% by massof Al₂O₃, forming the slurry into a plate shape, and drying the plate,and when a disk roll is formed from the base material, the disk roll hasa compression deformation of 0.5-0.3 mm when a load of 10 kgf/cm isimposed on a disk roll surface at 800° C.
 7. The method according toclaim 6, wherein the sinterable clay binder has particles having adiameter of 5 μm or larger.
 8. The method according to claim 6, whereina coating-forming substance is applied to the inorganic fibers in thebase material in an amount of 0.1 to 10% by mass based on a sum of theclay, filler, and inorganic fibers.
 9. The method according to claim 6,wherein the filler is contained in an amount of 5 to 60% by mass basedon the whole (total) amount of the base material.
 10. The methodaccording to claim 6, wherein the inorganic fiber contains SiO₂, CaO,MgO and Al₂O₃.